You’ve gotten some great suggestions so far. I especially like @merc81’s list of liberal arts colleges, although I agree with @doschicos that Whitman and Carleton are obvious omissions, and I would add Juniata and Connecticut College as well.
In your home state, all of the UCs are excellent options, as are most of the CSUs, especially Humboldt State. You may also want to take a look at the WUE schools like U Hawaii, U Montana, Washington State, etc.
Now, about Duke – I studied Earth & Ocean Sciences at Duke with a focus on marine science, so I am admittedly biased, but there are very few places better than Duke for undergraduate studies in environmental science and policy.
For one, the environmental science program at Duke is housed both in the Trinity College of Arts & Sciences and the separate Nicholas School of the Environment, and undergraduates can take graduate courses in the Nicholas School taught by faculty who teach and research exclusively in the Nicholas School. This makes it very different from most private universities and liberal arts colleges, which usually cobble together an environmental science program from cross-listed courses in the biology, geology, and chemistry departments. Similarly, students interested in environmental policy can take courses both in Trinity and Duke’s top-notch Sanford School of Public Policy.
Additionally, Duke has some amazing resources for students interested in environmental science and organismal biology, such as a 7000 acre research forest adjacent to campus, a lemur center with the largest collection of prosimians outside of Madagascar, and a marine lab in Beaufort, NC.
Unlike the biology program at Duke, which is quite large and somewhat impersonal, the EOS and environmental science majors involve considerably smaller classes (mine averaged 10-15 students) with faculty who are very enthusiastic about working with undergraduates. Many of the courses involve field trips and incorporate research opportunities (e.g. there’s a historical geology course that involves a trip to Yellowstone).